Polyimides

ABSTRACT

IMPROVED PRODUCTS ARE OBTAINED FROM THE POLYMERIZATION OF MIXTURES OF MONO-IMIDES AND BIS-IMIDES. THE COMPOSITIONS THUS OBTAINED HAVE IMPROVED PHYSICAL PROPERTIES AND HEAT RESISTANCE MAKING THEM ESPECIALLY SUITABLE IN VARIOUS COATING, INSULATING AND MOLDING APPLICATIONS.

United States Patent 3,738,969 POLYIMIDES Fred F. Holub, Schenectady,and Denis R. Pauze, Scotia,

N.Y., assignors to General Electric Company, Schenectady, N.Y.

No Drawing. Original application Apr. 25, 1969, Ser. No. 819,445.Divided and this application Apr. 30, 1971, Ser. No. 139,212

Int. Cl. (308g 20/20; C081? 31/04 US. Cl. 260-874 Claims ABSTRACT OF THEDISCLOSURE Improved products are obtained from the polymerization ofmixtures of mono-imides and bis-imides. The compositions thus obtainedhave improved physical properties and heat resistance making themespecially suitable in various coating, insulating and moldingapplications.

This application is a division of our copending application Ser. No.819,445, filed Apr. 25, 1969, entitled Polyimides.

This invention is concerned with improved polyimides. More particularlythe invention relates to a composition of mater comprising (1) amono-imide (hereinafter so identified) composition of the generalformula and (2) an imide selected from the class consisting of (a) animide of the general formula imide of Formula II (e.g., from 1 to 4mols) per mol of a diamino compound of the general formula and (c)mixtures of (a) and (b), where R is a member of the class consisting ofhydrogen, organic radicals (e.g., monovalent hydrocarbon radicals,halogenated organic radicals, etc.) and the radical, R is a divalenthydrocarbon radical of from 1 to 12 carbon atoms, R is a monovalenthydrocarbon radical of from 1 to carbon atoms, R is a member selectedfrom the class consisting of the 0:0 A l l 1\ /5 HC i HC- I! H2 H0 H0- H)m groupings, and halogenated, e.g., chlorinated derivatives of FormulasVI and VII, containing up to -6 or more halogens, Q is a member selectedfrom the class consisting of divalent organic radicals of at least 2carbon atoms (both halogenated and unhalogenated) including but notlimited to, e.g., divalent hydrocarbon radicals of up to 40 carbonatoms, and divalent groups consisting of two aryl residues attached toeach other through the medium of a member selected from the classconsisting of an alkylene radical of from 1 to 10 carbon atoms, -S, -SO

and -O, etc., X is a member of the class consisting of hydrogen,halogen, and the methyl radical, and m is 0 or 1, and the methyl groupin Formula VII can be present in place of any one hydrogen of themono-hydrogen-substituted carbons. It should be understood that Q inFormulas II and III may be the same or different.

The polymerization of maleimide either with heat or with both heat andperoxide is described in US. Pat. 3,317,678, issued June 16, 1964. Ithas also been found that N-substituted maleimides can be polymerizedwith either h'eat alone or with heat in the presence of organicperoxides, to give useful polymeric compositions. However, when suchN-substituted maleimides are polymerized by the above means, it has beenfound that the flexural strength of such products does not measure up tothe standards which are desirable or even required in numerousapplications. In addition, it has been found that though thepolymerization of such N-substituted maleimides yields products havingacceptable heat resistance and heat distortion temperatures, it would bedesirable, if possible, to improve these particular properties.

Unexpectedly we have discovered that the flexural strength, flexibility,heat resistance, and heat distortion temperatures of polymers ofN-substituted imides of Formula I can be measurably improved by theincorporation therein of effective amounts of a bis-imide hereinbeforedescribed, and thereafter heat-curing the mixture in the presence orabsence of sources of free radicals, irradiation with high energyelectrons, or other equivalent agents to give infusible, insoluble(e.g., in methylene chloride) products. In general We have found thatthe proportion of the bis-imide which is incorporated in the mono-imidecan be varied widely and can range, on a weight basis, from 5 to percentof the total weight of the mono-imide and the bis-imide. Theincorporation of amounts below 5 percent of the bis-imide effectsmeasurable improvements in the flexural strength of the polymerizedmono-imide.

Among the members which R in Formula I may represent are, for instance,hydrogen, monovalent hydrocarbon radicals, for instance, alkyl (e.g.,methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl, etc.) aryl(e.g., phenyl, dichlorophenyl, pentabromobiphenyl, tolyl, ethylphenyl,naphthyl, anthracyl, etc.); aralkyl (e.g., benzyl, phenylethyl,phenylpropyl, etc.) unsaturated aliphatic including unsaturatedcycloaliphatic (e.g., vinyl, allyl, methallyl, isobutylenyl, crotonyl,cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, ethynyl, propynyl,etc.), tolyl, ethylphenyl, etc.

Included among the mono-imide compositions of Formula I are, forinstance, maleimide, N-methyl maleimide,

VII

N-ethyl maleimide, N-phenyl maleimide hereinafter referred to as PMI,N-n-butyl maleimide, N-o-tolyl maleimide, N-o-biphenyl maleimide,N-monochlorophenylmaleimide, N-vinyl maleimide, N-allyl maleimide, N-cyclohexyl maleimide, N-decyl maleimide, N-propynyl maleimide, etc. Itwill of course be understood that in addition to maleimide andN-substituted maleimides, methylsubstitutcd mono-imides and halogenatedmono-imides can also be employed where the halogen, for example,chlorine, bromine, fluorine, etc., can range in number from 1 to 4 ormore haolgens on the carbon atoms adjacent to the carbonyl groups orcontained within the structure of the mono-imide.

The aforesaid class of mono-imides can be prepared quite readily. Forexample, maleimide or a substituted maleimide, for instance, amono-imide containing chlorine or a methyl radical on the carbon atom,may be prepared by reacting the appropriate anhydride of thedicarboxylic acid with the appropriate amine to form the monoamide ofthe acid and subsequently splitting off water from the monoamide. Forexample, in preparing N-phenyl maleimide, maleic anhydride is interactedas above with aniline and then with acetic anhydride and sodium acetate(to effect imidization) to give the desired N-phenyl maleimide.Similarly, the other N-substituted mono-imides can be prepared byemploying the proporiate amine for the purpose with the maleic anhydrideor other equivalent anhydride incorporating the desired R radical ofFormula I (the same applies to the use of the R radical for makingbis-imides), e.g., citraconic anhydride, itaconic anhydride,tetrahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride(hereinafter referred to as nadic anhydride; also known asendo-cis-5-norbornene-2,3-dicarboxylic anhydride), methyl-substitutedand halogen-substituted nadic anhydride, for instance,hexachloroendomethlyenetetrahydrophthalic anhydride, etc.

In addition to the above-described N-substituted monoimides,N-substituted mono-imides can be used where R corresponds to Formula IV.Representative of R as a monovalent hydrocarbon radical are the manyexamples of such monovalent hydrocarbon radicals given for R above.Among the divalent hydrocarbon radicals which R" may represent are, forinstance, preferably saturated alkylene radicals of from 1 to 12 carbonatoms (e.g., methylene, ethylene, isopropylidene, hexamethylene,decylene, etc.), divalent arylene radicals, for example, phenylene,ethylphenylene, naphthylene, etc., radicals. Included among suchorganosilyl-containing mono-imides may be mentioned, for instance,N-(trimethylsilylphenylene) maleimide, N-(dimethylphenylsilylethylene)maleimide, N-triphenylsilyl tetrahydrophthalimide, etc. Again thesecompositions may be prepared by reacting, for instance, maleicanhydride, methyl-substituted maleic anhydride or halogenated maleicanhydride with the appropriate amino triorganosilyl compound of theformula R!!! where R" and R' have the meanings above. Again silylatedderivatives of such compositions desired from itaconic, citraconic andtetrahydrophthalic anhydrides, in place of amleic anhydride may also beused in the practice of the present invention without departing from thescope thereof.

The bis-imides of the general Formula II can be varied widely dependingon the kinds of organic radicals which are present therein. Among thedivalent groupings which Q may broadly and more specifically representare, for instance, divalent saturated alkylene radicals of up to 40carbon atoms, for instance 1 to (e.g., ethylene, propylene, butylene,isopropylidene, hexylene, cyclohexylene, etc.), the divalent radical ofdiethylene oxide of the formula -CH CH O-CH -CH etc.); arylene (e.g.,m-phenylene p-phenylene, p,p'-biphenylene, dichlorophenylene,biphenylene methylene of the formula biphenylene oxide, biphenylenesulfone, biphenylene sulfide, keto biphenylene of the formula etc.) etc.Obviously, the arylene radicals may be attached to nitrogen through theortho, meta or para positions.

Typical examples of the bis-imides which may be employed with themono-imides or to make the reaction product with the diamino compound ofFormula III are, for instance, N,N'-ethylene-bis-maleimide,N,N-m-phenylene bis maleimide, N,N'-p-phenylene-bis-maleimide,N,N-hexamethylene-bis-maleimide,N,N'-p,p-diphenyldimethylsilyl-bis-maleimide, N,N' p,p'diphenylmethanebis-maleimide (hereafter referred to as BMI), N,N'-p,p-diphenylether-bis-maleimide,N,N'-p,p-diphenylthioether-bis-maleimide,N,N'-diphenylsulfone-bis-maleimide,N,N-dicyclohexylmethane-bis-maleimide, N,N-m-xylyl ene bis maleimide,N,N' p,p-benzophenone-bis-maleimide,N,N'-(3,3'-dichloro-p,p'-biphenylene) bis-maleimide, N,N-p,p-diphenylether-bis-endomethylene-tetrahydrophthalimide,N,N'-p,p-diphenylmethane-bis-tetrahydrophthalimide, etc. Halogenatedderivatives of such bisimides where halgen is on the anhydride portionof the imide and on an aryl nucleus can also be employed withoutdeparting from the scope of the invention, e.g., N,N'-(3,3'-dichloro-4,4' biphenyloxy) bis maleimide, N,N'-(3,3'-dibromo-4,4'-diphenylmethane) bis dichloromaleimide, N,N 4,4diphenylmethane-bis-hexachloroendomethylenetetrahydrophthalimide, etc.

Bis-imides which are especially suitable in the practice of the presentinvention are those corresponding to the general formula II II I R NRT-[Q] ,[T Il -N R C l l where R is a divalent alkylene radical of from 1to 10 carbon atoms or an arylene radical of from 6 to 20 carbon atoms,preferably selected from the class consisting of the arylene (e.g.,phenylene) and hydrocarbon-substituted arylene (e.g., phenylene)radicals, e.g., alkyl-substituted phenylene radicals (e.g., methyl,ethyl, propyl, etc., substituted phenylene radicals) and arylsubstituted (e.g., phenyl, tolyl, etc., substituted phenylene radicals)arylene radicals, where the number of substituents on the aryleneradical may range from 1 to 4, where R has the meaning given above, T isa member of the class of groupings selected from a divalent organicradical of at least two to as high as S0 or more carbon atoms,preferably selected from the class consisting of aromatic, aliphatic,cycloaliphatic, heterocyclic, combinations of aliphatic and aromaticradicals, and substituted hydrocarbon groups thereof, among which may bementioned phenylene radicals containing from 6 to 12 carbon atoms andthe radical where R is phenylene and alkyl-substituted phenyleneradicals and Z is a divalent grouping of the alkylene class and S, SO

and -O, X is a member selected from the class consisting of hydrogen,halogen and the methyl radical, and p and q are the same and are 0 or 1,R is the same as in Formula I. Typical of bis-imide coming from thescope of Formula X are those having the formulas Compositionscorresponding to the general Formula X and methods for preparing thesame are disclosed and claimed in the copending application of Fred F.Holub and Carl M. Emerick, Ser. No. 819,430 filed concurrently herewithand assigned to the same assignee as the present invention. Byreference, the disclosures of this latter application are made part ofthe disclosures of the instant application.

The above bis-imides of Formula II can be prepared by reacting two molesof maleic anhydride (or other anhydride required for making thebis-imides of Formula II) with one mole of a suitable diamino compound.Mixtures of anhydrides can be used if desired. Typical of the diaminocompound which may be employed for making the bis-imides of Formula IIor for making the reaction product between a diamino compound of FormulaHI and the bis-imides of Formula II may be mentioned, for instance,

meta-phenylene diamine; para-phenylen diamine;4,4'-diamino-3,5,3',5-tetramethyl-diphenyl methane; 4,4-d.iaminodiphenylpropane; 4,4-diamino-diphenyl methane; 4,4-diamino-diphenyl sulfide;4,4'-diamino-diphenyl sulfone; 3,3 '-diamino-diphenyl sulfone;4,4diamino-diphenyl ether; 4,4'-diamino-3,5,3,5'-tetrachlorodiphenylmethane,

2,6-diamino-pyridine; bis-(4-amino-phenyl) diethyl silane;bis-(4-amino-phenyl)phosphine oxide; bis-(4'aminopheny1)-N-methylamine;

6 1,5-diamino-naphthalene; 3,3'-dimethyl-4,4-diamino-biphenyl;3,3-dimethoxy benzidine; 2,4-bis-(beta-amino-t-butyl) toluene;bis-(para-beta-amino-t-butylphenyl) ether; para-bis-(2-methyl-4-amino-pentyl benzene; para-bis- 1,1-dimehyl-5-amino-pentyl)benzene; m-xylene diamino; p-xylylene diamine;bis(para-amino-cyclohexyl) methane; hexamethylene diamine;heptamethylene diamine; octamethylene diamine; nonamethylene diamine;decamethylene diamine; 3-methylheptamethylene diamine;4,4-dimethylheptamethylene diamine; 2,11-diamino-dodecane;1,2-bis-(3-aminopropoxy) ethane; 2,2-dimethyl propylene diamine;3-methoxyhexamethylene diamine; 2,S-dimethylhexamethylene diamine;2,5-dimethylheptamethylene diamine; S-methylnonamethylene diamine;1,4-diamino-cyclohexane; 1,12-diamino-octadecane;

2 2 3 2) 2 2) 3 2; z 2 a 2) s a; 2 2)3 3) 2)s 2; and mixtures thereof.

In addition to the mono-imide and the bis-imide having radicals Wherethe R is a grouping of the Formula V, R can also be either the groupingor halogenated derivatives therof, Where m is 0 or 1. In general thepresence of groupings VI and VII, or halogenated derivatives thereof canbe obtained by reacting maleic anhydride with, for instance, butadiene,pentadiene, cyclopentdiene (including methyl-substitutedcyclopentdiene), or halogenated derivatives thereof, by means of aDiels-Alder reaction before interaction of the latter maleic anhydridederivative with the monoamine compound or the diamino compound to formthe appropriate mono-imide or bis-imide.

We have found that in addition to using the monoimide, or the bis-imide,or the reaction product of the bis-imide and the diamino compound ofFormula III in the practice of the present invention, it is alsopossible to prepolymerize both the mono-imide and the bis-imide to astate of intermediate polymerization (short of the finally curedinfusible and insoluble state) similar to the B-stage ofphenol-formaldehye resins. Thereafter, the prepolymerized products canbe reacted either in the presence of heat alone or with an additionalamount of an organic peroxide or other source of free radicals to givethe finally cured, thermoset products. In particular, the use of suchprepolymerized compositions is especially advantageous in connectionwith the polymerizations involving the monomaleimides of Formula I. Thisis due to the fact that a number of these mono-imides have high vaporpressures and in certain applications, particularly in moldingapplications requiring a rapid conversion of the polymerizablecomposition to the finally cured state, elevated temperature arerequired to attain this objective. The use of abrupt high temperatureconditions tends to cause detrimental losses of some of the mono-imide.By converting the mono-imide to the prepolymerized product, this problemof undesirable volatilization (or sublimation as often is the case) canbe obviated.

This problem with the mono-imide is not as serious when the mono-imideis employed in applications involving coating techniques, where thetemperature used to convert the polymerizable mixture containing themono-imide can begin at a relatively low temperature and can progressgradually upward. Under such conditions of heating, the mono-maleirnideis caused to polymerize before reaching the temperatures at whichundesirable volatilization or sublimation occurs. Thereafter, the finalcure at the elevated temperatures does not encounter the problem ofexcessive loss of the mono-imide from the polymerizing mixtuer by virtueof its high vapor pressure.

Also, it may be desirable to prepolymerize the bisimides, and thisincludes the reaction product of the bisimides of Formula II with thediamino compound of Formula III. In addition, the mixture of themono-imide and the bis-imide may be prepolymerized in contact with eachother before use in applications. It has been unexpected found that byemploying the prepolymerized products, it is possible to have shortercuring cyles by employing higher temperatures.

The preparation of the prepolymerized products can be carried outgenerally by heating the imide, whether it is the mono-imide or thebis-imide at elevated temperatures ranging from about 75 to 200 C.,either with or without a source of free radicals, such as an organicperoxide, for periods of time ranging from a matter of from 10 toseconds to as high as one to two hours or more, maintaining theconditions of prepolymerization so that there is obtained a highermolecular weight product than what was initially employed. These highermolecular weight products can vary from liquids to solids depending onthe temperature. Generally at room temperatures (25-30 C.) ,they aresolids. The usual degree of polymerization which is desired is one wherethe problem of volatilization or sublimation no longer presents itselfand the prepolymerized product has not reached the thermoset infusibleand insoluble state. We have found that a useful end point ofprepolymerization is where the prepolymerized product has a flow point,that is the material becomes molten and starts to fuse, at a temperaturewithin the range of about 60 to about 250 C. This does not mean thatlower or higher flow points may not be useful or are contemplated. Itshould be recognized that the degree of polymerization will vary withthe starting maleimide, the temperature and time at which theprepolymerization reaction is carried out, the absence or presence of apolymerization moderator, and whether there is present or absent a freeradical initiator and also the amount of such free radical initiator.When employing a free radical initiator for prepolymerization purposes,the same free radical initiators can be used as when effecting the finalpolymerization to the cured, that is, thermoset, infusible and insolublestate.

In order to maintain control over the degree of prepolymerization, it isoften desirable to employ a polymerization moderator with the imideundergoing prepolymerization. These moderators are the usual ones whichare employed for controlling the length of chains of polymers made fromolefinic monomers. We have found that good control of prepolymerizationthat is molecular weight, degree of fusibility, etc., can be obtained byusing in the prepolymerizing mixture a small amount of oleic acid. Theamount of oleic acid which is used can be varied widely and as itincreases the degree of prepolymerization will be lower and the reactionwill proceed slower. Generally we may employ from about 0.01 to 2% ofthe polymerization moderator, such as the oleic acid, based on theweight of the inside or imides undergoing prepolymerization. In additionto the oleic & acid one can also employ other moderators for thepurpose, for instance, benzoquinone, linoleic acid, etc. The choice ofmoderator will depend on the unsaturated system being used; oleic acid,however, has been found to be acceptable in all systems tried.

For purposes of brevity and convenience, the term mono-imide and theterm bis-imide (which is intended to include not only bis-imides ofFormula II but reaction products of bis-imides of Formula II with thediamino compound of Formula III) are also intended to include withintheir definition prepolymerized products derived therefrom. Thus, whenreferring to or describing any uses made of the mono-imides Or thebis-imides, it is intended to include within the scope of suchreferences, the prepolymerized products derived therefrom.

The copolymerization of the mono-imide (or mixture of mono-imides) withthe bis-imide (or mixtures of bisimides) may be carried out merely byheating at temperatures ranging from about to 400 C. for the length oftime required to obtain the desired copolymerization. Generally,temperatures of the order of to 300 C. are adequate for the purpose. Theincorporation of organic peroxides or other free radical producingpolymerizing agents accelerates the rate of copolymerization. Among suchorganic peroxides may be mentioned dicumyl peroxide, benzoyl peroxide,dibenzoyl peroxide, tertiary butyl perbenzoate, cumene hydroperoxide,tertiary butyl hydroperoxide, 2,5-dimethyl-2,5 di(t butylperoxy) hexane,etc.; azo-bis-isobutyronitrile; etc. Generally the amount of cureaccelerator employed for the purpose can range from about 0.01 to ashigh as 5 percent or more, by weight, based on the total weight of themono-imide and the bis-imide.

It will be apparent to those skilled in the art that thecopolymerization of the mono-imide and the bis-imide can be carried outin the presence of a solvent, for example, N-methyl-Z-pyrrolidone,dimethylformamide, dimethylacetamide, etc. An important qualificationwhen using the solvent is that it be inert to the reactants and it havea sufficiently high boiling point to maintain a high enough temperatureat atmospheric pressure to effect the desired polymerization. The use ofpressure conditions is not precluded thus permitting lower boilingsolvents.

In addition to the copolymerization of the mono-imide and the bis-imide,other copolymerizable monomers containing at least one CH =C grouping(e.g., from 1 to 3) may be employed in positive amounts ranging up to 50percent or more, by weight, based on total weight of the mono-imide andbis-imide. Included among such vinyl monomers may be mentioned, forinstance, vinyl chloride; isobutylene, butadiene, isoprene,chlorotrifluoroethylene; Z-methylpentene-l; vinyl esters of Organiccarboxylic acid such as vinyl for-mate, vinyl acetate; acrylonitrile,styrene, vinyl methyl ether, vinyl methyl ketone; acrylic esters, suchas methyl-, ethyl-, butyl-, etc., esters of acrylic and methacrylicacids, etc.; diallyl phthalate, divinyl benzene, triallyl citrate,triallyl cyanurate, N-vinyl phthalimide, N- allyl phthalimide, N-allyltetrachlorophthalimide, etc.

The bis-imide prepared from the reaction of the bisimide of Formula IIand the diamino compound of the formula where Q has the meaning givenabove can be made in a number of fashions. Advantageously, one canemploy from about 1 to 4 moles of the bis-imide of Formula II for eachmole of the diamino compound. Generally the reaction between thebis-imide of Formula II and the diamino compound of Formula III isadvantageously carried out in a solvent such as dimethylformamide, N-methyl-Z-pyrrolidone, etc. The temperature of the reaction is notcritical and is favorably maintained within the range of fro-m about 90to 300 C. for times ranging from 2 minutes to as high as several hours,depending on the temperature, ingredients used and molar ratio of theingredients. If desired, the reaction product thus obtained from thebis-imide of Formula H can be additionally prepolymerized in the mannerpreviously described.

It is equally possible to effect the reaction between the bis-imide ofFormula H and the diamino compound by forming a mixture of the twoingredients without solvent and heating them at the desired reactiontemperature. In such circumstances, it would be necessary toeffectintimate dispersion and mixing of the ingredients.

Typical of the methods for making the reaction products of the bis-imideof Formula H and the diamino compound of Formula II are the followingexamples where all parts are by weight. Thus, in one instance, a mixtureof ingredients in a molar ratio of 1 mol of 4,4-diaminodiphenylmethane(8.29 parts) and 1 mol of BMI (15 parts) was heated at a temperature ofabout 120 C. for approximately 1 hour to give the desired reactionproduct; while another product was prepared by effecting reactionbetween 48.24 parts BMI and 12 parts 4,4-diaminodiphenyl oxide for 35minutes at a temperature of 195 C. and then for 1 hour at 195-200 C.under reduced pressure to give the desired reaction product.

It will of course be apparent to those skilled in the art that otherreaction products of a diamino compound and a bis-imide of Formula IIcan be obtained by varying the molar ratio of the reactants in eachinstance and employing similar conditions as recited above. The use ofthe same class of solvents as employed in connection with making themono-imides is not precluded. More specific directions for making thereaction products of the bis-imides of Formula II with the diaminocompound of Formula III may be found in French Pat. 1,555,564 grantedDec. 23, 1968; by reference, this patent is made part of the disclosuresof the instant application.

In addition to the foregoing ingredients, it is also possible to coreactat the same time that the copolymerization between the bis-imide and themono-imide takes place, other polymers and resins in amounts rangingfrom about 1 to 75 percent or more, by weight, based on the total weightof the aforesaid two imides. Included among such polymers may bementioned polyolefins (e.g., polyethylene, polypropylene, etc.)polystyrene, polyphenylene oxides such as shown in U.S. 3,306,875, epoxyresins such as shown in U.S. 2,840,540, polycarbonate resins such asshown in U.S. 3,028,365, silicone resins such as shown in U.S.2,258,218-222, phenol-aldehyde resins, polyimide resins such as shown inU.S. 3,179,633-634, polyarylene polyethers such as shown in U.S.3,332,909, etc., many of which are well-known and well-documented in theart.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation. All parts are byweight unless otherwise stated.

EXAMPLE 1 A series of copolymerizations were carried out employing PMIin combination with BMI in which the weights of the two ingredients werevaried. To each formulation was added one percent, by weight, dicumylperoxide, based on the total weight of the two maleimides. Each samplewas then heated to a temperature within the range of 220-270 C. over aperiod of about 2 hours to give heat-resistant infusible and insolublefilms. The cutthrough temperatures of the films obtained under theabove-described polymerization conditions were determined in accordancewith the method described in U.S. Pat. 2,936,296, issued May 10, 1960and assigned to the same assignee as the present invention. Thefollowing table discloses the formulations employed together with theresults of the cut-through tests.

1 Poor film-not self-supporting.

One of the unexpected discoveries of our invention involved finding thatthe heat stability of the mono-imide was materially improved whenvarying amounts of the bis-imide were incorporated, so that the finalheat stability was very close to the heat stability of the polymerizedbis-imide alone. This is important since the monoimide is generally moreavailable and less expensive than bis-imide. Specifically it was foundthat the stability in air, i.e., the weight loss of the polymerizedmono-imide when heated in air at elevated temperatures, was materiallyimproved and in most instances was almost equivalent to the low lossesencountered when the bis-imide alone was used. The following exampleshows the results of such tests.

EXAMPLE 2 In this example, varying amounts of PMI and BMI were mixedwith one percent, by weight, of the two maleimides of dicumyl peroxide.Thereafter, the mixture of ingredients was cast on a substrate andheated slowly while raising the temperature to about 220 C. over aperiod of about 2 hours. Each thermoset film thus obtained was heated inair at a constantly increasing temperature of 4.5 per minute until itwas determined at what temperature 10 weight percent of the polymerizedproduct had been lost. This point in polymer loss was taken for all theformulations as is illustrated in the following table:

TABLE II Temperature at which 10% weight loss occurred, C.

EXAMPLE 3 EXAMPLE 4 In this example, 22.5 parts PMI, 7.5 parts BMI,parts of asbestos fibers, and 0.3 part dicumyl peroxide were milled andpressed similarly as in Example 4 to yield a hard, substantiallyinfusible and insoluble molded product. Portions of this molded productwere tested and found to have a tflexural strength of 9130 p.s.i. and aflexural modulus of 2103 10 p.s.i. When the dicumyl peroxide wassubstituted with 0.3 part azobisisobutyronitrile and 0.08 partp,p'-diaminodiphenyl oxide added (for crosslinking purposes) and themixture molded as above, the sample had a flexural strength of 5340p.s.i. and a flexural modulus of 1.3 10 p.s.i.

EXAMPLE 5 15 parts PMI, 5 parts BMI, and 0.2 part dicumyl peroxide weremixed together and cast on a substrate and 1 1 heated similarly as inExample 1 to give a hard, infusible and insoluble film. This film wastested and found to have a cut-through temperature of 375 C.

EXAMPLE 6 This example, illustrating the copolymerization of anolefinically unsaturated monomer with compositions of the presentinvention, was obtained by compounding together 15 parts PMI, parts BMI,2.2 parts styrene, and

0.3 part dicumyl peroxide. The sample was cast as a Employing the sameconditions of milling and curing as in Example 1, parts PMI, 5 partsBMI, 2.2 parts polystyrene, and 0.2 part dicumyl peroxide yielded acured film which had a cut-through temperature of 400 C.

EXAMPLE 8 In this example, 15 parts PMI, 5 parts BMI, 2.2 parts of apoly-(2,6-xylylene) oxide polymer having a molecular weight above 20,000and an intrinsic viscosity of about 0.49 (prepared from 2,6-xylenol inaccordance with the disclosures of Hay Pat. 3,306,875, issued Feb. 28,1967, and assigned to the same assignee as the present invention) and0.2 part dicumyl peroxide were milled and cast into a film and curedsimilarly as in Example 1 to yield a thermoset, infusible, insolublefilm having a cut-through temperature of 375 C.

EXAMPLE 9 About 5.2 parts PMI and 11 parts BMI were compounded similarlyas in Example 1 and then heated for 21 minutes at 100 C. to give a cleartacky film. This film was irradiated with high energy electrons to adose of 2 10 rad. (using a high voltage apparatus with a peak voltage of800 kvp.), to give an infusible and insoluble stiff film having goodcut-through characteristics.

EXAMPLE 10 A bis-imide was prepared by reacting 5 mols BMI with 2 molsof p,p'-diamino diphenylmethane at 160 C. for about 25 minutes to give abis-imide which is believed to be composed of compositions havingwithintheir scope structures such as XVIII alone or further reactionproducts with the diamino compound or with the bis-maleimides. 15 partsof this bisimide were milled with 15 parts PMI, 70 parts of asbestosfibers, and 0.3 part dicumyl peroxide and then molded at 165 C. for 5minutes at 2000 p.s.i. This yielded a hard, infusible and insolubleproduct which had a fiexura] strength of 3700 p.s.i. When the filler wasomitted and a film cast on a substrate and heated similarly as inExample 1, it gave a thermoset film having a cut-through of 320 C.

EXAMPLE 11 In this example, 22.5 parts PMI was compounded with 7.5 partsof various bis-imides, 0.3 part dicumyl peroxide and 70 parts asbestosfibers, molded and the flexural strengths of the insoluble infusiblemolded products determined. The compounding and molding additions wereessentially the same as those described in Example 4. The followingtable shows the different bisimides employed and the results of theflexural tests.

TABLE III Flexural Sample I strength, No. Bis-imide p.s.i.

1 N,N-p,p-diphenylmethane-bis-tetrahydro- 2, 500

phthalimlde. 2 N,N-m-phenylene-bis-maleimide 6,500 3 N,N-p,p-diphenylether-bis-maleimide 9, 4 N,N-p,p-diphenylsulfone-bis-maleimide. 6, 900

EXAMPLE 12 In the following example, different mono-imides other thanthe PMI described above, were employed with the BMI. TheN-phenyltetrahydrophthalimide was prepared by reactingtetrahydrophthalic anhydride with aniline. The N-phenylnadicimide wasprepared by reacting aniline with Nadic anhydride(endo-cis-5-nonborene-2,3-dicarboxylic anhydride). The following tableshows the two difierent mono-imides employed together with the flexuralstrengths for each of the samples which were compounded and moldedsimilarly as in Example 4. In each instance, the formulations of Samples1 and 2 comprised 15 parts of the mono-imide, 15 parts of the bis-imide,70 parts of asbestos fibers, and 0.3 part dicumyl peroxide. Reference ismade to Example 4 where N-ethylmalemide was reacted similarly as above.

13 EXAMPLE 13 In this example a mixture of PMI and BMI was milled withan asbestos fiber filler and one percent, by weight, of the mixture ofmaleimides, dicumyl peroxide, and molded at a temperature of 225250 C.,for 1.5 to 2 hours at 200 p.s.i. After molding, samples of each moldedproduct were tested for flexural strength. For comparison, a sample wasalso molded of the PMI above containing one percent, by weight, thereofof dicumyl peroxide and a corresponding amount of asbestos fiber filler.The following table shows the formulations employed in each instance andthe flextural strengths of the molded samples.

TABLE V Parts Flexural Sample strength, No. PMI BMI Filler p.s.i.

EXAMPLE 14 TABLE VI Parts Flexu- Flexural Sample Other As- Perrel,modulus No. PMI BMI imide bestos oxide p.s.i. p.s.i.

15 a 15 70 0.75 7,300 1 78 10 15 b 15 70 0.75 8,500 1 58Xl0 7. 5 70 0.75 6,000 1. 6X10 7.5 7.5 35 0.3 10,750 2.4X10

N-phenylimide of Nadic anhydride (see Table IV for formula).

11 N-phenyltetrahydrophthalimide.

Other imide was N-allylphthalimide; also contained 35 parts choppedglass fibers.

EXAMPLE 15 In this example, the mono-imide and bis-imide of Example 1were mixed with various polymers and asbestos fibers and afterincorporating dicumyl peroxide as curing agent, the mixtures ofingredients were molded similarly as in Example 4 tested for flexuralstrength. The basic formulation included 18 parts PMI, 6 parts BMI, 70parts asbestos fibers, 0.24 part dicumyl peroxide, and 6 parts of thespecific polymer. The following table shows the various resins whichwere employed in the aforesaid mixture of ingredients together with theflexural strength of the cured molded products which in each instancewere infusible and insoluble.

a This sample was included to show a comparison of using monomericstyrene in the formulation in place of polystyrene in the same quantity.

EXAMPLE 16 In this example, various formulations were made from 6 partsPMI, 1.5 parts BMI, 0.075 part dicumyl peroxide, and 0.83 part or 2parts of various resins and, in one instance, monomeric styrene. Themixtures of ingredients were compounded and cast into films and curedsimilarly as in Example 1. Samples thereof were then tested for TAB LEVIII 0. cutthrough 10% 0. cut- Sample through No. Resin 20% a Thisformulation comprised 33 parts PMI, 33 parts BMI, 33 parts of thephenolic resin and 1 part dicumyl peroxide.

EXAMPLE 18 A series of advanced or prepolymerized N-phenyl maleimide andN,N'-p,p'-diphenylmethane-bis-maleimide were prepared by heating each ofthe maleimides under a nitrogen blanket in a constant temperature bathmaintaiued either at C. or 170 C., employing in some instances oleicacid as a moderator, and in other instances a peroxide in the reactionmixture.

The time for terminating the prepolymerization was taken as the point atwhich solution of all the ingredients became evident and a viscousliquid material was formed at the temperature at which prepolymerizationwas carried out. Thereafter, each prepolymerized product (which alsoincluded a product made by copolymerizing N-phenyl maleimide with theN,N'-p,p'-diphenylmethane-bis-maleimide) was compounded with a filler,specifically the asbestos fibers, and then further heat treated at atemperature under the same conditions as recited in Example 4. Samplesthus molded were tested for flexural strength and flexural modulus. Thefollowing Table IX shows the ingredients used to make the prepolymerizedproducts and the properties of the prepolymerized products.

TABLE IX Parts Flow Oleic Benzoyl Tem Time, point, PMI BMI acid peroxide0. seconds C.

EXAMPLE 19 In this example, prepolymerized PMI was prepared by heatingthe PMI with 0.05%, by weight thereof of benzoyl peroxide for 12 minutesat 90 C. while stirring. This yielded a viscous material having a flowpoint of about 90 C. This prepolymerized PMI will hereinafter beidentified as PPMI. In addition, prepolymerized BMI was prepared byheating BMI without a peroxide for about 20 minutes at C. to give ahighly viscous product which was a solid at room temperature. Thisproduct will hereinafter be identified as PBMI. Each of theprepolymerized compositions was mixed with each other or withnon-prepolymerized PMI or non-prepolymerized BMI together with anasbestos fiber filler. To each formulation was added 1%, by weight,dicumyl peroxide, based on the total weight of the polymerizableingredients. The samples, which were compounded and molded similarly asin Example 4 were then tested for flexural strength and flexuralmodulus. In one example, the product of prepolymerization of a mixtureof PMI and BMI, the preparation of which is shown in Sample No. 5 ofTable IX (Example 18) was also milled with filler and peroxide similarlyas above and its properties were also determined. An additional example(Sample No. 6) was compounded from PPMI, BMI and styrene again employingabout 1%, by weight, dieumyl peroxide, based on the total weight of thethree copolymerizable ingredients; in the case of this latter example,no filler was added but instead the mixture was cast onto a solidsubstrate and the surface was heated gradually and uniformly to 200 C.over a l-hour period, and the cut-through temperature of this cured filmwas then determined. This same method was used to obtain cut-throughtemperatures of unfilled formulations. The following Table X shows theformulations and the results of tests conducted on the cured productstherefrom.

cured state, makes these compositions especially unique. When used asfilms or when made into molded products, these polymer, includinglaminated products prepared therefrom, not only possess excellentphysical properties at room temperature but they retain their strengthand excellent response to work-loading at elevated temperatures for longperiods of time. The fact that they have high decomposition points, wellabove 400 C., and in some instances above 500 C., indicates a wide rangeof commercial utility for these products. These polymers in particularresist fusion when exposed to temperatures of 400 to 500 C. for extendedperiods of time while still Cut through was determined on formulationsbased on Samples 1 to 5, but omitting the filler, and curing similarlyas in Sample No. 6.

b Prepolymerized mixture of Sample No. 5 of Example 18. Contained partsstyrene.

EXAMPLE 20 In this example, the xylenol sulfone ester bismaielmrde ofFormula XII (obtained by heating 2 moles p-maleimidobenzoyl chloride and1 mole, 2,6-xylenol sulfone of the formula CH3 CH3 if HO- S -OH I i CH:CH3

for 6 hours at 155 C. until HCl ceased to evolve) was mixed with PMI inan equal weight ratio and to the mixture was added 3%, by weight,benzoyl peroxide, based on the weight of the two maleimides. The liquidmixture thus obtained was cast on a substrate and heated uniformly withincreasing temperature from 70 to 250 C. over a period of about 60minutes. There was thus obtained a cured, thermoset film which wasinsoluble in methylene chloride.

EXAMPLE 21 In this example PMI alone or PMI and BMI were mixed withasbestos fibers and 1%, by weight, dieumyl peroxide based on the weightof the maleimides was added by milling the ingredients at about 70 C.Thereafter each formulation was heated at 165 C. for 5 minutes at about2000 p.s.i. to give a cured solid product in each instance. Samples ofeach of the cured materials were then tested for fiexural strength andfor heat distortion. The following Table XI shows the formulationsemployed together with the test results on the cured samples.

TABLE XI Parts Heat Sample Asbestos Flexural, distortion 0. PMI BMIfibers p.s.i. temp. C.

for physicals.

a This molded sample was heated at 250 C. for 333 hours before testingretaining an exceptionally high proportion of their room temperaturephysical properties. The ability to make [fusible or soluble precursorsof the finely cured products makes them especially suitable in thepreparation of shaped articles such as films, molded products, etc.whereby using conventional techniques, the mixture of copolymerizedingredients can be converted in situ to the finally cured, infusible andinsoluble state.

Films formed from the polymeric compositions of this invention may beused in applications where films have been used previously and inaddition films therefrom can be used in applications where films in thepast have not been especially suitable. They serve effectively in anextensive variety of wrapping, packaging and bundling applications.Thus, the compositions of the present invention can be used inautomobile and aviation applications for decorative and protectivepurposes, and as high temperature electrical insulation for motor slotliners, in trans/formers, as dielectric capacitors, as coil and cablewrappings (form wound coil insulation for motors), for packaging itemsto be exposed to high temperatures or to corrosive atmospheres, incorrosion-resistant pipes and duct work, for containers and containerlinings, in laminating structures where films of the present compositionor where solutions of the claimed compositions of matter are applied tovarious heat-resistant or other type of materials such as asbestos,mica, glass fiber and the like and superposing the sheets one upon theother and thereafter subjecting them to elevated temperatures andpressures to effect flow and cure of the resinous binder to yieldcohesive laminated structures.

Films made from these compositions of matter can serve in printedcircuit applications, [for instance, as backings by coating the filmsmade from such cured compositions with a thin layer of copper oraluminum either by coating the metal with the curable orheat-convertible compositions herein described and then by heating atelevated temperatures to convert the product to the completely curedstate, or by laminating a metal sheet to the cured resinous composition.The circuit design is then covered by a protective coating and the extrametal is etched off followed by washing to prevent further etching. Anadvantage of making such circuit boards is that the base film is stableto heat so that it can be connected to other components by a dipsoldering technique while in contact with the other components withoutadversely affecting the resinuous support base.

Alternatively, solutions of the curable compositions herein describedcan be coated on electrical conductors such as copper, aluminum, etc.,and thereafter the coated conductor can be heated at elevatedtemperatures to remove the solvent and to effect curing of the resinouscomposition thereon. If desired, an additional overcoat may be appliedto such insulated conductors including the use of polymeric coatings,such as polyamides, polyesters, silicones, polyvinylformal resins, epoxyresins, polyimides, polytetrafluoro-ethylene, etc. The use of thecurable compositions of the present invention as overcoats on othertypes of insulation is not precluded.

Porous films can also be prepared by compounding the compositions ofthis invention with water-soluble salts, such as sodium benzoate,molding this mixture at elevated temperatures and pressures to formsheets which can be treated with water to leach out the water-solublesalt.

Applications which recommend these resins include their use as bindersfor asbestos fibers, carbon fibers, and other fibrous materials inmaking brake linings. In addition, molding compositions and moldedarticles may be formed from the polymeric compositions in this inventionby incorporating such fillers as asbestos, glass fibers, talc, quartz,powder, wood flour, finely divided carbon, silica, into suchcompositions prior to molding. Shaped articles are formed under heat, orunder heat and pressure in accordance with practices well known in theart. In addition, various heat-resistant pigments and dyes may beincorporated as well as various types of inhibitors depending on theapplication intended. Socalled resistance or semiconducting paints mayalso be made from the compositions by incorporating in solutions ordispersions of the curable polymeric mixture, controlled amounts ofconducting materials such as carbon, silicon carbide, powdered metal,conducting oxides, etc. in order to impart to the cured paint theparticular degree of resistance of semiconduction.

Among the specific applications for which the compositions hereindefined may be employed include as finishes for the interiors of ovens,clothing driers, as finishes for cooking utensils, mufiler liners,liners for high temperature equipment including liners for hot Waterheaters, as protective coatings for fragile or brittle substrates suchas protective coatings for high temperature bulbs, glass equipment,etc., as flame-retardant paints, as belting for use in high temperatureconveyors, etc.

The compositions herein defined may suitably be incorporated in othermaterials to modify the properties of the latter or in turn theirproperties may be modified by the incorporation of the other material.For example, they may be compounded with substances such as natural orsynthetic rubbers; synthetic resins such as phenol-aldehyde resins,urea-aldehyde resins, alkyd resins, etc.; cellulosic material such aspaper, inorganic and organic esters of cellulose such as celluloseacetate, cellulose ether; such as methyl cellulose, ethyl cellulose,benzyl cellulose, etc. In some instances, plasticizers and othermodifying agents may be used in combination therewith to yield productswhich when applied to a base member and air dried or baked have a highdegree of heat-resistance due to the presence of the compositions hereindefined.

It will of course be apparent to those skilled in the art that inaddition to the compositions specifically referred to in the foregoingexamples, other mono-imides, and bis-imides, many examples of which havebeen described previously, may be employed without departing from thescope of the invention. The mono-imide or bis-imide employed is notcritical and all that is needed are groups corresponding to Formulas V,VI and VII in the imides where R and Q are representative genericmonovalent organic radicals and divalent organic radicals, respectively,of broad and non-critical scope.

In addition, other copolymerizable monomers containing at least one CH=C grouping or other resins and polymers, again many examples of whichhave been given previously, may be used within the scope of theinvention. Other peroxides, and cure accelerating agents, as well asionizing radiation, may be employed, and obviously the conditions ofcopolymerization and cure may be varied within wide limits.

Processing advantages in making and converting the compositions of thepresent invention to the thermoset, infusible, insoluble state can oftenbe realized if one employs a diamino compound with the combination ofthe mono-imide and the bis-imide, many examples of said diaminocompounds having been given under Formula III. Persons skilled in theart will have no difficulty in understanding how to use the diaminocompounds of 'Formula III, especially in view of Example 5. Anadditional method which has proved applicable for the purpose involvesmixing the mono-imide with the diamino compound and thereafter with thebis-imide and then heating the mixture of ingredients. As a specificinstance, 13.8 parts of PMI was mixed with 7.93 parts of 4,4-diaminodiphenyl methane at about C. under nitrogen atmosphere for about5 minutes, and thereafter about 36 parts of BMI was added and theheating continued at this temperature for an additional 40 minutes togive a resinous composition which could be heated at C. with about 1%,by weight, thereof dicumyl peroxide to give a tough film that did notsoften even at temperatures of around 280 C. It will be apparent tothose skilled in the art that other diamino compounds can be used withthe other mono-imides and bis-imides, including the prepolymerizedderivatives thereof, to obtain im- I and (2) an imide compositionobtained by heating at a temperature in the range of from about 90 C. to300 C. a bis-imide of the general formula l ll and a diamino compound ofthe general formula wherein said mixture thereof is from 1 to 4 mols ofthe bis-imide per mol of the diamino compound, where R is a member ofthe class consisting of hydrogen, and monovalent hydrocarbon radicals, Ris a member selected from the class consisting of groupings, Q is amember selected from the class consisting of divalent organic radicalsand divalent groups consisting of two aryl residues attached to eachother 19 through the medium of a member selected from the classconsisting of two aryl residues attached to each other through themedium of a member selected from the class consisting of an alkyleneradical of from 1 to 10 carbon atoms, S, -S0=,,

and O,' and X is a member of the class consisting of hydrogen, halogen,and the methyl radical, and m is 0 or 1.

' 2. A composition as in claim 1 wherein the diamino compound is4,4diaminodiphenylmethane.

3. A composition of matter consisting essentially of (a) the fusibleproduct obtained by heating N-phenyl maleimide to a temperature in therange of from about 78 to 200 C. and (b) the fusible reaction productobtained by heating the mixture ofN,N'-p,p'-diphenylmethane-bis-maleimide and 4,4-diaminodiphenylmethaneto a temperature in the range of from about 90 C. to 300 C.

4. A composition as in claim 3 containing a filler therein.

5. The heat-treated product of claim 3.

References Cited UNITED STATES PATENTS 2,743,260 4/1956 Tawney 26078 UA2,818,405 12/1957 Kovacic 26078 UA 3,137,678 6/1964 Jousset 26078 UA3,352,832 11/1967 Barr et a1 260 -78 UA 3,380,964 4/ 1968 Grundschoberet a1.

26078 UA 3,406,148 10/1968 Sambeth et a1. 26078 UA FOREIGN PATENTS951,025 3/1964 Great Britain 26078 UA HAROLD D. ANDERSON, PrimaryExaminer US. Cl. X.R.

204-159.22; 26041 R, 47 CZ, 47 UA, 78 UA, 827, 844, 857 R, 873, 875

